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In Reply to: RE: Speaker cabinet foam lining material posted by madisonears on December 16, 2014 at 21:47:08
The speaker cabinets are the tall, triple-folded enclosures of a horn loaded design. There are two foam slabs per speaker, both are 9" wide. One is about 24" long while the other is about 18" long. The originals were not stapled or glued in, instead they slide into the bottom of the cabinet and rest against the slanted vertical walls of the interior.
In the link to Royal Device provided below, take a look at the photo that is fourth from the top. On the right hand side of that photo, you can see the end of one slab of dark grey foam peeking out of the bottom of that speaker cabinet. You can also view the the ends of two internal chambers or folds. Two foam slabs per speaker, one for each internal chamber.
In these latest photos, the manufacturer has chosen to show the speakers mostly without foam inserts, which leads me to believe that he designed the foam inserts as optional, removable "tuning" devices. I would need foam slabs for both speakers for balanced sound and/or experimentation purposes, and presently I am missing one set of foam slabs.
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Pretty cool speakers, definitely worth fussing over. I would buy new foam for both speakers to match.
I expect that the foam is present to absorb higher frequencies of the back wave of the driver. In that case, it is important whether the foam is open or closed cell, and its density is secondary. Open cell foam is expensive to make and much harder to find. There is a simple test to determine which is which. I think if you can easily blow through a layer of foam, it's open cell, but a closed cell will be more resistant. Better check on that. I'm willing to bet the PE stuff is closed cell. If the original is open cell, you do NOT want to change to closed. If the original is closed cell, nearly any similar foam will work.
If it sat free in the enclosure, then I'd guess that's what will work for the replacements. Sometimes the foam works more efficiently when both sides are exposed. You might at least make a trial with two-sided tape or something easily removed.
Peace,
Tom E
Thanks for the great advice.I'm not sure if the foam is open cell or closed cell, I'll have to check when I get the pieces out of storage. I will ask Parts Express about the composition of their stuff.
I've been running both speakers without the foam liners, and so far I haven't noticed any ringing or unusual resonances. Mine are the MK II model with sturdy cabinets made of nicely finished Birch ply, rather than the solid Pearwood of the newer models. If you scroll about 2/3 of the way down on the photo page I linked above, you can see several speaker cabinets identical to mine "stacked" against the back wall of the listening studio. The openings on the bottoms of the cabinets are normally covered by removable black screens.
I am hesitant to use adhesives of any kind because the foam slabs must be coaxed upward into place from the bottom of the cabinet. There is no way to press down evenly on them once they've been inserted because of the depth of the cabinet. Besides, I like having the option of removing the foam slabs at will.
Edits: 12/17/14 12/17/14
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